1. Field of the Invention
The present invention relates to an optical transceiver unit used for transmitting and/or receiving an optical signal. In the field of electronics and communication, in order to transfer or interchange a great volume of information at a high speed within or between electronic equipment, an optical signal is transmitted through an optical fiber as a transmission line. An electric signal carrying information is converted into an optical signal for transmission and the optical signal is converted into an electric signal for processing the information.
Therefore, an opto-electric converter (optical receiver unit) and an electro-optical converter (optical transmitter unit) which are small-sized, high-speed, highly reliable and also easy in manufacturing and operation, are in great demand.
2. Description of the Related Art
An optical transceiver unit including the optical receiver unit and optical transmitter unit in a one-piece construction, is acknowledged as prior art.
FIGS. 1A-1C are top, front and side plan views, respectively of a casing body.
The casing body 1 is made by bending a sheet of metal along four sides there of to form a case with a bottom 2 surrounded by a wall and by welding an L-shaped metal strip 3 to the bottom 2 to form a partition wall 3a for dividing the case into left and right chambers. Rectangular holes, or slots, 4, 5 are bored in the respective chambers.
Four curved projections 8 are extended and extend inwardly, two each from right and left sidewalls 6, 7 close to the bottom 2, to position and support a printed circuit board. The upper surface of the projection 8 is equal to that of the partition 3 in height above the bottom 2. A projection strip 9 is formed by punching, at a distance equal to the thickness of the printed circuit board above each of the projections 8, thereby to have the printed circuit board inserted therebetween. Four projections 11 extrude (extend) outwardly, two each from the sidewalls 6, 7 close to the bottom 2. Projections 12 are formed in the respective centers of the side walls 6, 7 by punching and bending such that the bottom of each declines outwardly for latching a casing cover.
Corresponding to the right and left chambers formed by the partition 3, holes 14 are provided in the front wall 13, respectively for mounting an optical receiver module and an optical transmitter module therein. A bend 16 is provided on the partition wall 3a to position the front end of the printed circuit board. The casing body 1, which is made of structural sheet steel, is nickel-plated to improve conductivity and to prevent rusting.
FIG. 2 shows the casing body 1 having a printed circuit board 17, an optical receiver module 18 and an optical transmitter module 19 mounted therein.
The four-layer printed circuit board 17 is mounted such that it fits in an area enclosed by the side walls 6, 7, the rear wall of the casing body 1 and the bend 16 of the partition 3. It is supported in position on the respective upper surfaces of the projections 8 and the partition wall 3a. Then, the projections 9 of the right and left sidewalls 6, 7 are bent over the printed circuit board 17 and soldered to respective ground patterns 21 printed thereon.
For easy understanding, electronic parts mounted on the printed circuit board 17 are not shown in FIG. 2. The printed circuit board 17 has lead terminals 22 arranged in a line and projecting downwardly through the rectangular holes 4, 5, to connect to a main printed circuit board. On one side of the casing-body front wall 13, the optical receiver module 18 is fastened to a flange 24 of a metal case 23 with screws 25. The metal case 23 houses a photo diode for performing opto-electric conversion, built in a metallic container.
Wires for supplying a bias voltage to the photo diode, outputting an electric signal and outputting ground signals for the output signal and the metallic container are soldered to a connection pattern 26 printed on a side of the printed circuit board 17. An end of an optical fiber 27 is connected to the optical receiver module 18 and the other end to an optical connector 28.
On the other side of the casing-body front wall 13, the optical transmitter module 19 is fastened to a flange 32 of a metal case 31 with screws 33. The metal case 31 houses a laser diode for performing electro-optical conversion, built in a metallic container. A wire for supplying power to the laser diode and a wire for connecting to a monitor laser diode are soldered to connection patterns 34 printed on the side of the printed circuit board 17. An end of an optical fiber 35 is connected to the optical transmitter module 19 and the other end to an optical connector 36.
FIGS. 3A-3C are inside, front and side plan views, respectively of a casing body.
The casing cover 41 is made by bending a sheet metal along the four sides there of to form a case surrounded by a wall. An L-shaped metal strip is welded to an upper surface 42 to form a partition wall 43a dividing the case into two components. Rectangular holes 46 are bored in the respective centers of the right and left sidewalls 44, 45. Two holes 47 are bored at the respective front and rear edges of the sidewalls 44, 45 close to the aperture (i.e., top opening) of the case. A gap 49 is provided on the right and left sides of the front wall segments, 48. The casing cover 41, which is made of the structural sheet steel board, is nickel-plated for finishing to improve conductivity and to prevent rusting.
FIG. 4A is front plan view of an assembly of the conventional optical transceiver unit (optical connecters 28, 36 not shown). FIG. 4B is a front sectional view of an assembly of the conventional optical transceiver unit.
In FIG. 4A, the casing cover 41 fits on the the casing body 1 to cover its opening. The optical receiver module 18 and optical transmitter module 19 within the gaps 49 provided on the front side of the casing cover 41.
In FIG. 4B, the projection strips 12 provided on both of the casing-body sidewalls 6, 7 fit in the rectangular holes 46 provided on the casing-cover sidewalls 44. A flat surface of the rectangular hole 46 engages with a side of the projection 12 to prevent the casing cover 41 from coming off the casing body 1. The projections 11 provided on the casing-body sidewalls 6, 7 fit in the front and rear holes 47 of the casing-cover sidewalls 44, 45 to prevent backlash and reenforce electric contact between the the casing body 1 and casing cover 41. Since the casing-body partition wall 3a and casing-lid partition 42 electrically isolate the right and left chambers, each accommodating the optical transmitter circuit and optical receiver circuit mounted on the printed circuit board 17, electromagnetic interference between the circuits is reduced.
In each chamber, a resin-covered IC bear chip is mounted under the printed circuit board 17. On a side of each compartments, lead terminals 22 project downwardly for connecting the optical transceiver unit to a main printed-circuit board. In the conventional optical transceiver unit as described above, the casing body 1 and the casing cover 41 are both made of sheet metal and to mount the optical receiver module 18 and optical transmitter module 19, the flanges 24, 32 are provided and fastened to the casing body with screws 25, 33.
Therefore, it is a problem that a large area is required for mounting the modules, accordingly rendering the unit large-sized and heavy. It is another problem that a burdensome manufacturing process is required for mounting the printed circuit board 17 on the casing body 1, for example, for providing the partition 3, the projections 8 and the bend 16 for positioning the printed circuit board 17, and for bending the projection 9 and soldering the wires to the printed-circuit-board ground patterns 21.